The invention relates to a concrete lining element for a drilled tunnel, which element is formed as a ring segment and is internally reinforced, and a plurality of which ring segments can be joined together to form a ring, and a plurality of rings can be joined to form the lining for the drilled tunnel and wherein, in order to couple adjacent rings at the intermediate ring joint, each element is provided at one side bordering the ring joint with at least one projection, and at the opposed side with a corresponding recess to intermate with the projection of an adjacent element.
This kind of known, prefabricated drilled tunnel lining elements is used to line the inside of drilled tunnels. The rings are formed of a plurality of joined elements which extend in the circumferential direction of the drilled is tunnel, while said rings are joined in the longitudinal direction of the drilled tunnel. Between adjacent rings there is a so-called ring joint.
When a tunnel is being drilled in relatively soft ground as, for instance, is usually the case in the Netherlands, it is essential that the separate drilled tunnel lining elements are joined together in order to limit deformation of the drilled-tunnel lining and consequently of the tunnel. However, such reciprocal connections generate forces in the drilled tunnel lining elements that may result in unwanted damage. It has been shown, for example, that due to the loads that have to be absorbed, cracks may develop starting from the recess, which is detrimental to the strength of the joint. Removal (repair) of the occurring damage involves high costs.
The object of the present invention is to improve a lining element for a drilled tunnel of the above-mentioned kind such, that the strength of the element at the joint between adjacent elements can be appreciably improved. In order to achieve this objective the drilled tunnel lining element according to the invention is characterized in that the height of the projection, respectively the depth of the recess on the respective side is between 30 and 60 mm, and in that the projection, respectively the recess at the transition from its top, respectively its bottom to its side walls, possesses rounded corners, having a radius of rounding of between 5 and 50 mm.
Embodying the drilled tunnel lining element in this manner has shown that the joint between the adjacent elements can be three to five times as strong as with conventional known drilled tunnel lining elements, with the height of the projection, respectively the depth of the recess being, for example, 19 mm, while the radius of the rounding at the transition from the top of the projection, respectively the bottom of the recess to its side wall is not very significant. Thanks to the design according to the invention higher loads can be absorbed without exhibiting any undesirable damage to the drilled tunnel lining elements.
In accordance with a preferred embodiment the design of the drilled tunnel lining element may be further optimized by arranging that the aperture angle of the sidewalls of the projection, respectively the recess is between 30xc2x0 and 45xc2x0.
The aperture angle of the side walls is understood to mean the angle between the side walls and the line perpendicular to the respective side. This measure, in combination with the measures mentioned earlier regarding the height, respectively the depth and radius of rounding result in a drilled tunnel lining element with excellent characteristics.
The drilled tunnel lining elements to which the present invention relates are usually of the kind wherein the projection is formed like a truncated pyramid with a substantially rectangular base. In such a case the ratio between the length and the width of the base is at most 1.3. By limiting this ratio it is possible to keep the length of the projection at the base as small as possible, which then naturally also applies to the recess. In this manner there is sufficient space around the recess for applying a suspension reinforcement, so that the strength of the drilled tunnel lining element, especially at the side provided with the recess, can be further improved.
In this respect it is further preferable that the internal reinforcement extends in the direction of the element""s side provided with the recess, at least to the plane through the bottom of the recess. This measure also contributes to improving the strength of the drilled tunnel lining element at the side provided with the recesses.
Within the above-mentioned ranges for the projections height, respectively the depth of the recess, the radius of rounding and the aperture angle of the side walls, particular values have been shown to be especially advantageous. For example, a particularly preferred height of projection, respectively depth of recess is 40 mm. The radius of rounding in a favourable embodiment is 15 mm, and an aperture angle of 35xc2x0 will provide an advantageous result.
It should be noted that there is a connection between most of the above-mentioned measures according to the invention. In combination they lead to an optimal result, although each individual measure already improves the drilled tunnel lining element compared with a known existing element.